Abstract
Sedentary behaviour has become a well-known risk factor for cardio-metabolic disease. Results from observational studies indicate that regularly breaking sedentary behaviour with light bouts of physical activity is associated with lower risk of cardio-metabolic disease. It has been proposed that breaking sedentary behaviours improves cardio-metabolic risk primarily through processes involved in postprandial metabolism, in particular attenuating the glucose and insulin response. Abnormal glucose and insulin metabolism in the postprandial period is a well-known indicator of cardio-metabolic diseases. Therefore, the aim of the current study was to investigate the effects of two days of prolonged sitting and regular activity breaks (2 minutes brisk walking every 30 minutes), with and without physical activity (30 minutes continuous brisk walking) at the end of the first day, on postprandial glucose and insulin metabolism on day two.
A randomised crossover, laboratory based study was conducted in Dunedin, New Zealand between June 2014 and November 2015. Thirty-six healthy, normal weight adults (Mean (SD) BMI 23.8 (4.0)) aged 18 to 35 years participated in four interventions. The interventions were conducted over two consecutive days each, separated by at least 5 days and consisted of: 1) Prolonged Sitting, during which participants sat continuously for 7.5 h and 6 h on two days of clinic visits; 2) Physical Activity, during which participants remained seated for 7 h on Day 1, followed by a 30 minute continuous brisk walk, and remained seated for 6 h on Day 2; 3) Regular Activity Breaks, during which participants interrupted their sitting every 30 minutes with 2 minutes of brisk walking on a treadmill, performing a total of 14 walks on Day 1 (28 accumulated activity minutes) and 10 walks on Day 2 (20 accumulated activity minutes); 4) Regular Activity Breaks plus Physical Activity, during which participants interrupted their sitting every 30 minutes with 2 minutes of brisk walking on a treadmill for 7 h on Day 1, which was followed by a 30 minute continuous brisk walk, and Day 2 was completed identical to the Regular Activity Breaks intervention. Glucose and insulin metabolism was measured in response to a mixed meal fed to participants at 0 h on Day 2 consisting of 0.71 g.kg-1 carbohydrate, 0.70 g.kg-1 fat, 0.32 g.kg-1 protein and 43.24 kJ.kg energy. Blood samples were collected from a venous cannula at baseline and hourly for 5 h, with additional samples collected at 30 and 45 minutes after the meal was fed. Postprandial responses for plasma glucose and insulin were calculated as total area under the curve (tAUC).
Postprandial glucose response was not significantly different between interventions. Postprandial insulin tAUC response decreased from 140.6 uU.mL-1.h during Prolonged Sitting to 125.6 uU.mL-1.h during Regular Activity Breaks (Ratio of Difference 0.89; 95% CI 0.80, 0.99; P = 0.037), 120.0 uU.mL-1.h during Physical Activity (Ratio of Difference 0.85; 95% CI 0.75, 0.96; P = 0.008), and 109.3 uU.mL-1.h during Regular Activity Breaks plus Physical Activity (Ratio of Difference 0.78; 95% CI 0.69, 0.88; P < 0.001). There was also a significant decrease in postprandial insulin response between Regular Activity Breaks interventions without (125.6 uU.mL-1.h) and with Physical Activity (109.3 uU.mL-1.h) i.e. Regular Activity Breaks plus Physical Activity (Ratio of Difference 0.87; 95% CI 0.79, 0.97; P = 0.008).
The lack of effect of any of the interventions on glucose response is in contrast with previous studies, and may indicate a lack of sufficient glucose challenge provided to the sample of young, healthy adults. The combined Regular Activity Breaks plus Physical Activity intervention was the most effective (i.e. greatest reductions) at lowering postprandial insulin response in comparison to Prolonged Sitting. These findings indicate that over two days breaking prolonged sitting with short bouts of activity combined with a singular 30 minute bout of activity has sustained metabolic benefits on postprandial insulin response.